1. Field of the Invention
This invention relates to a locking/unlocking state confirming device in which the most recent locking/unlocking state of a lock can be indicated on a key so that its user can confirm visually the locking/unlocking state of a house or a car by looking at the key.
2. Description of the Related Art
Many types of so-called locking/unlocking state confirming devices having the above function are proposed at present. One such known locking/unlocking state confirming device is disclosed in Japanese Patent Application No. 145163/1992. Such device is a good idea in that it does not require a battery for indicating the locking/unlocking state.
A construction of such locking/unlocking state confirming device will be briefly described. As shown in FIG. 1, a first drive magnet 5 and a second drive magnet 6, which comprise respective permanent magnets, are secured to a front end face of an outer sleeve 2 of a cylinder lock 1 at locations symmetrical with respect to a key way 4 open to an inner cylinder 3. The first and second drive magnets 5 and 6 are mutually oppositely magnetized in an axial direction of the inner cylinder 3. For example, if the surface of the first drive magnet 5 is an N pole, that of the second drive magnet 6 is an S pole.
A magnet holding chamber 11 is formed in that area within a non-magnetic key bow 8 attached to a key bow portion of a key 7 which is proximate to a front end face opposite to the cylinder lock 1 (see FIG. 2) and which is generally in alignment with the drive magnets in a radial direction of the cylinder lock 1 when a stem 9 of the key 7 is inserted in the key way (see FIG. 3). A suction plate or holding plate 12 of magnetic properties is firmly secured to a front inner surface of the magnet holding chamber 11. A prismatic indicator magnet 13 is magnetically drawn to and held by the holding plate 12.
In general, a lock device comprising a cylinder lock and a key is designed such that when the key 7 (specifically, the stem 9 of the key 7) is inserted into the key way 4 of the cylinder lock and turned, for example, clockwise for locking, the key 7 is required to be turned counterclockwise for unlocking. In this way, the indicator magnet 13 within the key bow of the key which is caused to approach the first magnet 5 for locking is, in turn, caused to approach the remaining second magnet 6, which has a different magnetic polarity than the first magnet 5, when the lock is to be unlocked. In the above example, since the key 7 is turned clockwise for locking, the indicator magnet 13 is caused to approach the N pole of the first drive magnet 5 and then gradually is moved away therefrom. This is the same whether the key is withdrawn at a location where the key is turned, for example, 180 degrees, or whether the key is withdrawn after it has been turned clockwise by a predetermined angle and then turned counterclockwise by such predetermined angle. Accordingly, if the key 7 is turned clockwise, for example, by 90 degrees when the lock is in a locked position, the S pole of the indicator magnet 13 is drawn to the N pole of the first drive magnet 5 as shown in FIG. 4, and is held by the holding plate 12 in the sate shown in FIG. 4. Thereafter, a further turning operation of the key 7 in an effort to bring the indicator magnet 13 away from the first drive magnet 5 does not make any change of the state shown in FIG. 4. The same is true when the key 7 has been withdrawn from the key way.
As shown in FIG. 4, that side surface of the indicator magnet 13 denoted by q is painted, for example, green and the other side surface denoted by 4 is painted, for example, red. Accordingly, when the green side surface of the indicator magnet 13 within the magnet holding chamber 11 is visually recognized through a viewing window 14 open to one side surface of the key bow of the key 7 as shown in FIG. 3, it is known that the cylinder lock 1 is in a locked position. The same is true when the user removes the key and see it at his/her visiting cite. On the other hand, in order to unlock the cylinder lock 1 in a locked position, the key 7 is inserted into the key way 4 of the cylinder lock 1 and turned counterclockwise. The result is that when the key 7 is turned counterclockwise by about 90 degrees, the first drive magnet 5 if FIG. 4 is switched to the second drive magnet 6. In other words, the N pole of the drive magnet 5 of FIG. 4 is inverted (not shown) to its S pole. As a result, the S pole of the indicator magnet 13 repulses the S pole of the second drive magnet 6 and floats over the holding plate 12. On the other hand, the N pole of the indicator magnet 13 is drawn to the S pole of the second drive magnet 6. That is, the indicator magnet 13 is turned 180 degrees about a rotary axis vertical to the sheet surface of FIG. 4, so that the red-colored side surface denoted by r can be seen through the viewing window 14 (see FIG. 3). In this way, the key 7 can indicate the unlocking state of the cylinder lock 1. The angular position of the indicator magnet 13 showing the unlocking state of the like is stably maintained by the indicator magnet 13 secured to the holding plate 12.
However, the above-mentioned operation of the locking/unlocking state confirming device is the operation originally intended, but such device actually does not operate in that manner. The disclosure of the above Japanese application apparently is based on theoretical considerations without carrying out any substantial experiments. Actually, the indicator magnet 13 does not work at all even if the first and second drive magnets 5 and 6 are mutually switched.
The reason is that, since the holding plate 12 of magnetic properties exists between the drive magnets 5, 6 and the indicator magnet 13, magnetic flux from the drive magnets is cut off by the holding plate 12. Therefore, the indicator magnet 13 does not receive any magnetic repulsive force and magnetic attractive force from the drive magnet, even if the indicator magnet 13 is caused to approach the drive magnet 5 (6). Another reason is that the existence of the holding plate 12 necessitates a substantial distance between the drive magnet 5 (6) and the indicator magnet 13, and a magnetic force is weakened in inverse proportion to the square (second power) of the distance between the drive magnet 5 (6) and the indicator magnet 13.
At any rate, the inventor of the present invention has confirmed through experiments that the invention according to the above-mentioned Japanese Patent Application does not exhibit the originally intended effects.